The present invention relates to a fixation device permitting the orientation of the part held, which device is more specifically used in the field of external bone fixation appliances.
For the reduction of bone fractures, for example, a technique of fixing pins in the bone was in fact developed long ago, which pins are either extended in the neighboring bone or are secured in an external fixation device including a frame in order to hold the fractured segments in place.
Frame appliances comprising arcuate cradle elements are known, such as the ones described in U.S. Pat. No. 4,365,624.
The sectional shape of such an arcuate element has also been analyzed, and preference given to a form described in U.S. patent application Ser. No. 821,671, filed Jan. 23, 1986, which form permits the realization of numerous and extensive possibilities for mounting pins as well as frame rods or other connecting parts or members.
The elements of which such external fixation means are composed must be designed with two aims. Firstly, they must be as simple as possible to facilitate the surgeon's work during the operation while permitting a wide range of possible positionings. Secondly, they must afford a thoroughly rigid and secure fixation, so that the reduction of the fracture will not be compromised during convalescence.
There are known positioning and securing devices comprising jaws clamping a part, the contacting surfaces of the jaws and of the part to be clamped therewith being realized so as to be somewhat roughened, for example as obtained by sandblasting. These devices are generally satisfactory, but with time the rough surfaces wear smooth and the roughness is lost. As the surfaces in contact become smoother, the clamping becomes less and less effective.
Securing devices have also been proposed that comprise planar surfaces with grooves. Such plane surfaces commonly clamp a cylinder or a sphere of plastic material. Alternatively, grooves may likewise be provided on the part having a rounded portion to be clamped. Such a device is described, for example, in PCT World Patent Application No. 83/02554. This device gives good results, but the plastic part deteriorates quickly so that its service life is relatively short.